1. Field of the Invention
The present invention relates generally to electronic article surveillance (EAS) systems and EAS tags used in such systems and, more particularly, to an EAS tag polling system in which a plurality of tags are polled by a base station to determine whether a positive response or a negative response is to be associated with each one of the tags.
2. Description of the Related Art
Electronic article surveillance systems have become commonplace for both inventory control and theft prevention of merchandise. For example, to prevent theft an EAS tag is affixed to an item of merchandise that has been made available for consumer selection and purchase within a retail store. The tag may be removably attached to the item of merchandise desired to be protected, or permanently or semi-permanently affixed to such item. Upon purchase of the tagged item at a checkout counter, the tag is removed or otherwise disabled by a sales clerk or other store employee upon payment being tendered for the item. However, should one attempt to shoplift the tagged item, such as by surreptitiously concealing the tagged item, an alarm will sound when the tag is passed through a detector which is typically located in close proximity to an exit of the store.
A removably attached tag generally includes a key latch mechanism on one hinged portion of the tag housing that locks to a pin projecting from an opposing hinged portion of the tag housing. The pin is passed through the item, typically a garment, and into the lock mechanism of the tag. Upon sale of the tagged garment, a sales clerk uses a unique key or decoupler to unlock the pin from the lock mechanism so that tag can be removed.
A permanently or semi-permanently attached tag generally is glued or otherwise affixed to the item itself, to a paper fiber box containing such item or to shrink wrap sealing such box. When affixed directly to the item or to the box, the tag may be placed inside either one where it is not visible and, therefore, its presence may not be known to one who would attempt to shoplift such item. This type of tag is most prevalent for use with small items such as audio and software CDs, and electronic items and components. Upon sale of the item, the sales clerk needs to disable the tag so that the consumer can safely pass the detector located at the exit of the store without triggering the alarm, as would otherwise occur should the tag not have been previously disabled.
The EAS tags of the type described above typically include a passive resonant LC circuit enclosed within a nonmetallic housing. The LC resonant circuit includes a capacitor and an inductor typically formed as metallic foil elements on a suitable substrate. Such construction allows for the tag to be relatively small and inconspicuous, especially for the permanent or semi-permanent type tag. To disable the permanently or semi-permanently attached tag, the sales clerk passes the tag through a relatively strong RF signal that is picked up by the inductor windings. In turn, a current surge is induced in the windings and this current is of sufficient amplitude to “break” one or more of the resonant circuit elements, typically the capacitor, or a resistive element or fuse within the circuit. Features and descriptions of EAS tags and systems of the type as described above may be found in whole or in part in U.S. Pat. No. 4,774,504; U.S. Pat. No. 5,949,336; U.S. Pat. No. 5,955,951; U.S. Pat. No. 5,979,196; U.S. Pat. No. 5,982,284; U.S. Pat. No. 6,254,953; and U.S. Pat. No. 6,304,182.
As set forth above, a detector is placed in close proximity to each exit of the store in order to alert store employees and security of an attempt to shoplift the tagged item. The detector may typically include an RF transmitter and an RF receiver such that an RF signal is developed across the path of the exit. When the tag passes through the RF signal (such tag not having been permissibly disabled in the case of the permanent or semi-permanent tag) an AC current will be induced in the inductor windings at the resonant frequency of the LC circuit. This current then causes a further RF signal to emanate from the inductor windings that will be received at the receiver of the detector. This further RF signal will be detected as a modulation of the primary RF signal developed by the transmitter of the detector. Upon detection of this modulation, an alarm can then be sounded.
A limitation and disadvantage of the above described EAS tags and systems is that detection of the attempted theft of the tag item does not occur until the item is already at the exit of the store. Absent an immediate security response upon the alarm being sounded, the perpetrator may readily leave the store with the tagged merchandise and evade apprehension.
Another disadvantage and limitation of the forgoing is that the theft protection provided thereby is relatively easy to defeat. For example, the key or decoupler required to remove the key lock of the removably attached tag may be possessed by one desirous to shoplift the item to which the tag is attached or by a dishonest employee who would otherwise have permissible possession of the key or decoupler. With the tag impermissibly removed from its item while in the retail store, the item can then be surreptitiously carried past the detector and from the store.
The permanently or semi-permanently attached tag, although it needs to be carried past the detector in an attempt to shoplift the item to which it is attached, is also relatively easy to defeat. In this case, the item need only be surreptitiously placed into a metal enclosure, such as a foil lined paper sack or a foil lined purse. The foil thus functions as an RF shield preventing the primary RF signal from the detector reaching the LC resonant circuit of the tag. Even if some RF energy does reach the tag through the foil shield, the tag would produce such a low level of RF output energy, if any, that any RF perturbation from the tag is most likely to be shielded by the foil shield. Accordingly, it is highly unlikely that any perturbation to the primary RF signal would be detected.
Variations to the foregoing EAS tags and systems are also known. For example, in U.S. Pat. No. 6,801,130, an EAS tag is designed to be placed on the packaging for the item in the manner such that the packaging cannot be opened until the tag is removed. The device that removes the tag is further enabled by a point-of-sale cash register only after the sale for such item has been recorded. However, unless such tag renders the item non-operative, or can only be impermissibly removed by causing damage to such item, such tag exhibits the same disadvantages and limitations of the EAS tags and systems described above.
A magnet circuit may also be used in such tags instead of a LC resonant circuit. For example, a magnetic EAS tag is described in U.S. Pat. No. 5,821,859, in which magnetic elements are closely spaced perpendicularly along an amorphous wire or strip. Each element, such as formed by magnetic ink, is magnetically saturated or left demagnetized. The magnetic elements thus form a binary code along the wire or strip, wherein such code may be used to provide a unique ID for the tag. The tag ID can be magnetically read at the point-of-sale for inventory control. The tag also contains a longer length of magnetic wire, which perturbs a magnetic field in a magnetic gate, also typically located in close proximity to the exit of a retail store to provide theft deterrence. However, such magnetic tag exhibits the same disadvantages and limitations as the RF EAS tags and systems described above.
A disadvantage and limitation of the above described magnetic EAS tag for inventory control is that manual intervention is required to read such tag. This manual intervention may occur at the point-of-sale, as described above, or by manually placing a magnetic reader next to each tag while in situ. The latter described method may be extremely laborious and time-consuming, or further subject to fraud by a dishonest employee.
A disadvantage and limitation common to of all of the above described EAS tags and systems is that such tags and systems relying upon detection of the tag when the tag crosses the boundary of the designated area. The detectors used in such systems define the boundaries of such area.
One prior art system to overcome this boundary condition is configured to detect a possible theft or other security breach while the tag is still within the designated area. For example, in U.S. Pat. No. 6,255,958, an active electronic tag includes a transmitting circuit configured to turn on when an attempt is made to remove the tag impermissibly from the item to which is attached. When turned on, the transmitter circuit transmits an RF signal that is conventionally detected to cause an alarm to sound. The system described in the '958 patent also includes a proximity sensor that detects when the tag is out of range of the sensor, which also causes the alarm to sound.
A disadvantage in limitation of the tag and system described in the '958 patent is that such system requires one proximity sensor to be placed relatively closely to each tag being monitored. Accordingly, such system is primarily useful for tagging stationery objects, such as artwork in the museum, and not for items of general merchandise that may be randomly and permissibly carried by consumers in the secure designated area of a retail establishment prior to check out.
One particular disadvantage and limitation that the above described EAS tags and systems do not address is when the tagged items need to be regularly moved between a stockroom and a display area within a retail store. For example, small expensive items such as gemstones, jewelry, watches and the like are typically removed from locked display cases during the hours the retail establishment is closed and placed in a vault or other secure stockroom. Since the boundary of the protected area is at the store exit, a theft occurring by a dishonest employee during the time the items are being removed from the display case may not be immediately detected. It is accordingly desirable that the boundaries between these different areas within the store are protected as well as the boundary at the exits of the store.
Accordingly, there exists a need to provide an EAS tag and system that overcomes one or more of the above described disadvantages and limitations. There exists a further need to provide an EAS tag and system that detects an attempt to conceal surreptitiously an EAS tag while such tag is being otherwise permissibly moved within the boundaries of a protected designated area. There it is still a further need to provide an EAS tag and system that facilitate inventory control without the need to read the tag at the point-of-sale or manually placing a reader next to each tag. There exists yet another need to provide an EAS tag and system that allows such tag to cross permissibly the boundaries of one or more designated areas. There exists still yet another need to provide an EAS tag and system that allows such tags to provide continuous protection while the tag is in transit between protected areas.